That is how I transport my kite buggy too Ben.
I remove the tow ball/goose neck and my rack slides into the Reece Hitch receiver, which takes a 2" x 2" square tube. Yes they are still imperial sizes. 50mm x 50mm is a sloppy fit. You can still buy structural 2"x 2" x 1/4" wall square RHS in Australia.
The horizontal 3/4" locking pin secures it and a 1/2"lock bolt on a diagonal corner stops it from rattling around in the receiver.
The rear window of the canopy can still be opened and additional tail lights have now been added at the top outer corners behind the glass window.
I should relocate my number plate too as my buggy now has much larger wheels. 12" x 21" Beach racer fatties.